Writing in The Journal of Experimental Biology, researchers Sandie Millot, Pierre Vandewalle and Eric Parmentier from the University of Liège, Belgium, say that their study of red-bellied piranhas showed that the fish "became quite vocal as soon as they entered into a confrontation."

And the team identified three sounds: A "bark" when the researchers reached into their tanks (yes, theydid have to visit a hospital and one of Millot's fingers was "nearly cut in half"); a "drum-like sound when fighting for food;" and "a softer 'croaking' sound produced by their jaws when they snap at each other." (National Geographic describes that last sound as more like teeth gnashing.)

The fish use "muscles attached to their swim bladders" to make the drum-like sounds, the Journal says.

According to Parmentier, two or three of the 25 piranha species are known to make such sounds.